However, after she wrote home to her mother in November, authorities said they were convinced the teen could be in “grave” danger -- with the possibility that someone coercing her to stay away from home.

PHOTO: North Conway teen, Abigail Hernandez, has been missing for two months.

"We have said from the beginning and we continue to believe that this was a 14 year-old girl who went missing in October," Associate Attorney General Jane Young told ABC News. "She was gone for nine months. She didn't have the means to orchestrate and facilitate this on her own."

Hernandez was reunited with her family Sunday.

"The long and short of it is, quite honestly, we are just happy that she's home safe and sound right now," FBI Special Agent in Charge Kieran Ramsey said Monday.

The criminal investigation into Hernandez’s disappearance will continue. Authorities remain tight-lipped on specifics, and no arrests have been made. Young did confirm that the Hernandez family is being cooperative but would not say if Abigail has been interviewed by police.

Investigators and Abby's mother, Zenya Hernandez, detailed the case on a missing person's website and wrote that she did not have a history of running away from home.

Conway Police Dept.

PHOTO: Abigail Hernandez, 15, was last seen leaving Kennett High School in North Conway, N.H., Oct. 9th, 2013.

Following her disappearance, rescuers fanned out for days over the region’s heavily forested terrain. Police also searched by air, stopped traffic and handed out missing posters and used boats. For search volunteers such as Amanda Smith, the teen’s safe return was welcome news.

“I am just so happy that she is home,” Smith said. “I can’t wait to go see her and her mom.”

The girl’s family released a statement thanking everyone who helped with the search.

“Abby is safely home with her mom and sister!! Thank you to everyone who has shared fliers, offered help and support,” the family said.

ABC News' Dan Good and The Associated Press contributed to this report.